Suzaku broadband observations of galactic black hole binaries: Low/hard state spectra of GRO J1655-40

Hiromitsu Takahashi, Yasushi Fukazawa, Tsunefumi Mizuno, Ayumi Hirasawa, Shunji Kitamoto, Keisuke Sudoh, Takayuki Ogita, Aya Kubota, Kazuo Makishima, Motohide Kokubun, Takeshi Itoh, Arvind N. Parmar, Tadayasu Dotani, Ken Ebisawa, Sachindra Naik, Tadayuki Takahashi, Kousuke Ohnuki, Tahir Yaqoob, Lorella Angelini, Yoshihiro UedaKazutaka Yamaoka, Taro Kotani, Nobuyuki Kawai, Masaaki Namiki, Takayoshi Kohmura, Hitoshi Negoro

Research output: Contribution to journalConference articlepeer-review


The Galactic black-hole binary GRO J1655-40 was observed with Suzaku on 2005 September 22-23, for a gross time span of ∼1 day.The source was detected over a wide and continuous energy range of 0.7-300 keV, with an intensity of ∼50 mCrab in the 1.5-12 keV band. At an assumed distance of 3.2 kpc, the 0.7-300 keV luminosity is calculated to be ∼ 4.4 × 10 36 ergs s-1. The source was in a typical low/hard state, since its overall spectrum was dominated by a power-law component with a photon index of ∼1.7. The source intensity gradually decreased by 20% during the observation, involving little spectral changes above ∼3 keV. However, at softer energies, the amplitude of variability was somewhat enhanced. This indicates the presence of an independent soft component. The spectra in the hard energy band reveal a high-energy spectral cutoff, with an e-folding energy of ∼200 keV which is suggested to be higher than those observed from typical black hole binaries in the low/hard state.

Original languageEnglish
Pages (from-to)325-332
Number of pages8
JournalEuropean Space Agency, (Special Publication) ESA SP
Issue number622 SP
Publication statusPublished - 2006 Jul
Externally publishedYes
Event6th Integral Workshop - The Obscured Universe - Moscow, Russian Federation
Duration: 2006 Jul 22006 Jul 8


  • Accretion disks
  • Black hole physics
  • Stars: individual (GRO J1655-40)
  • X-ray: binaries

ASJC Scopus subject areas

  • Aerospace Engineering
  • Space and Planetary Science


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